Cloner
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methylene iodide
I tried using potassium iodide and acetone to convert methylene chloride into methylene iodide. On reflux temperature for several days, only 5% was
converted.
Synthetikal refers to using a 'soda bottle' and heating it. I assume the soda bottle is used to withstand pressure and the temperature is much higher
than what I used. Does anyone have experience with this reaction?
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Nicodem
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From your mentioning of a 'soda bottle' I asume you are refering to this method. Note, that it is taken from a paper published in 1921 and they still quite improvised at those times. There is the reaction
temperature missing so I would assume the bottle was immersed in a boiling water bath which would mean the internal pressure was less that 5 atm which
is still reasonably well supported by a 'bottle' (though I would avoid sticking around it too much). If you try this, mind to use a thick walled
bottle and mind that the stopper should be of a material that does not soften with DCM and acetone. I would suggest a reagent bottle (thick wall and
teflon stopper) which, in my experience, already proved succesfull in similar reactions involving autogenous pressure generated by EtOH, iPrOH and
similar at up to 120°C (I used the 100ml Fluka bottle).
You used KI which I suspect is less ideal for a chloride swap with the iodide in the NaI/acetone method. The method calls for NaI and the reason is
its (relatively) high solubility in acetone vs. the very low solubility of NaCl. This might be another reason of the low yield in addition to the much
lower reaction temperature which is certanly the major one to blame.
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Cloner
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I am absolutely positive that KI or NaI are both sufficiently soluble to make no difference while the chlorides are insoluble. s you say, the main
problem is the exchange. When a sample is taken and mixed with chloroform, KI precipitates from the acetonic solution of the reagents.
So basically you are using the GLASS fluka bottles that liquids come in at 5 bar? I don't mind dodging PET other than for losing the reactants but do
mind glass shards flying around Come to mind, I have an aluminum vessel used
for diethylether. If this can meets EU regulations, it might withstand a lot of pressure...
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Nicodem
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It is the relative difference in NaI vs. NaCl and KI vs. KCl solubilities that drives the reaction toward the iodo compound. As you probably know the
chloride anion is a stronger nucleophyle than the iodide in dipolar aprotic solvents, so the mechanistical equilibrium lies in favor of CH2Cl2. It is
only the fact that NaCl is practically insoluble in acetone at all temperatures that drives the reaction against its equilibrium. I don't know which
pair of these salts has a better solubility difference but since NaI is always used I suspect the pair of sodium salts was found optimal. (I'm not
saying that KI does not work, only that it might not work equally well.)
But anyway, the main problem is the reaction temperature. Be careful with an aluminum vessel if it is not coated - CH2Cl2 and CH2I2 can react with Al,
especially at 100°C. A reagent bottle is safe enough in my experience. It does not break, instead if the pressure rises too much the stopper starts
leaking gas. But just in case, keep away as much as possible.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Ullmann
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| Quote: | | As you probably know the chloride anion is a stronger nucleophyle than the iodide in dipolar aprotic solvents, so the mechanistical equilibrium lies
in favor of CH2Cl2. |
In ethanol the iodide anion is a stronger nucleophile than the chloride anion, also it is a better leaving group. From Clayden p441:
Relative rates (water = 1) of reaction of nucleophiles with MeBr in EtOH:
F- : 0
H2O : 1
Et3N : 1400
PhO- : 2000
Br- : 5000
EtO- : 60000
I- : 120000
PhS- : 50000000
| Quote: | | Nucleophiles like R3P: and RS-, the ones that react well with saturated carbon, are referred to as soft nucleophiles and those that
are more basic and react well with carbonyl groups referred to as hard nucleophiles. These are useful and evocative terms because the
soft nucleophiles are rather large and flabby with diffuse high-energy electrons while the hard nucleophiles are small with closely held electrons and
high charge density. |
| Quote: | | In SN2, iodide ion is one of the best nucleophiles towards saturated carbon because it is at the bottom of its group in the periodic table and its
lone-pair electrons are very high in energy. This is in spite of the very low basicity of iodide (HI pKa=-10). It reacts rapidly with a variety of
alkyl derivatives and alkyl iodides can be made by displacement of chloride or tosylate by iodide. |
| Quote: | | But why are these alkyl iodides made? They are needed for reactions with other nucleophiles in which iodide is again displaced. As well as being one
of the best nucleophiles for saturated carbon, iodide ion is one of the best leaving groups from saturated carbon. Yields are often higher if the
alkyl iodide is prepared than if the eventual nucleophile is reacted directly with the alkyl tosylate or chloride. |
But I agree the driving force in fielkenstein is one of solubility of each salt.
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Nicodem
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True. In ethanol and other protic polar solvents the iodide is a much stronger nucleophyle, but in acetone (and other aprotic dipolar solvents like
DMSO, DMF etc) it is the reverse.
Check the chapter "2. Solvent Effects" in Reactions of Alkyl Halides
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Klute
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| Quote: | Ok, I figured I could just pop this thread back to life rather than start a new one or continue in the short question thread...
methylene iodide can be a pretty usefull reagent, and is much more ffective than DCM under atmospheric conditions. Beside the iodide swap mentionned
above, it seems CH2I2 is generally made from CHI3 by using sodium aresenite, not a nice thing to play with. I've looked briefly into tow other method
of preparation from CH3I.
From iodoform and sodium ethoxide (KOH could possibly be used also): I've translated the revelant parts of an old Ann. article where iodoform
is reacted with 3 eqs of EtONa to form CH2I. No yields mentionned though:
Partial Translation of Ann. Chim. Phys., , 53 (3), 313 (1858)
[Quote]
Memoire on methylene iodide
by M. Alexandre BOUTLEROW
Professor of Chemistry at the University of Kasan
Considering that sodium ethoxide has a similar constitutuion to sodium hydroxide, I thought it would be interesting to compare the action of iodine on
these two compounds, so I studied the action of this simple compound on the ethoxide.
When powdered iodine is added in portions to cristallized sodium ethoxide, a vigorous reaction immediatly occurs, followed by heat evolution: the mass
liquifies and turns brown; but after a while, as soon as all the iodien has reacted, this coloration disappears. By continuing the addition of iodine,
we fianlly obtain a thick and yellow magma.
For the complete decomposition of the ethoxide to occur, and the brown color indicating excess I2 to persists, more than one equivalent of iodine for
each equivalent of ethoxide are required. When the mixture is distilled on a water bath, some alcohol is collected, containing a heavy oily compound
which can be seperated by addition of water. When diluted with water, the distillation residu dissolves nearly entirely, leaving some iodoform. The
aqueuse solution contains some sodium iodide and sodium formate, but no iodate. By evaporating this solution and distilling the inorganic residu with
tartaric acid, some formic acid can be detected in the distillate, using a silver salt. At the same time the alcohol seems to be regenerated in this
recation, that we can surely express by the following equation:
8 C4H5O2Na + 16 I = C2HNaO4 + 6C4H5O2H + 3 C2HI3 + 7NaI (?? apparently they hadn't worked out the structures completely yet!)
By using one equivalent of iodine for each equivalent of ethoxide, and by gradually distilling to near-dryness, a quite large amount of oil is
obtained in the distillate, compared to the amount of iodoform that stays in the residu; on the other hand, the latter is found in exces if the yellow
magma is directly diluted with water without been submitted to distillation. These observations seem to indicate that the oily compound is only a
by-product from the action of sodium ethoxide on iodoform. I had to study this action.
On solid iodoform container in a large container, is added a mildly-concentrated solution of sodium ethoxide obtained by dissolution of sodium metal
in a rather large volume of absolute ethanol. Brief warming in a hot water bath is needed to get the reaction started. The mixture quickly heats up to
a vigorous reflux, with no gas evolution. Once the reaction is finished and the liquor is no longer alkaline, a new portion of ethoxide is added and
the mixture is heated; these operations are repeated until 3 equivalents of ethoxide (based on the amount of sodium dissolved) are added. At this
moment, the liquid is slightly basic, but remains so. It is heated for another few minutes, then diluted with water. A yellowish, milky solution is
obtained, and after a moment a brown oily substance crashes out of solution. When the reaction is well performed, the oil contains little impurities;
but is heating is excessive, or that a too alrge excess of ethoxide has been employed, the oily substance is contaminated with a brown decomposition
product, pulveresent and insoluble in alcohol.
On the opposit, unreacetd iodoform remains if heating was insufficient or that too little ethoxide was added.
Exces alcali seems to prevent deposition of the product; the addition of a few drops of acid easily induces deposition. After 24h, all the oil has
crashed out, and the aqueous solution become colorless. The oil is decanetd, washed and readily steam-distilled.
The compound thus obtained is identical to the oil obtained by the action of iodine on sodium ethoxide, as confirmed by elemental analysis. When
distilled, it boils around 181°C, but is partially decomposed, loosing iodine. The distilled product is always colored, and during the distillation
the head temperature increases as the residu darkens more and more.
Afetr having been distilled in steam and dried over fused calcium chloride, the compound thus obtained presents the following caracteristics: it is a
yellowish oil, very refractive, possesing the surprising property of hardly wettening glass; it's smell is analogous to that of chloroform, and
reminds taht of ethyl iodide, it taste is very sweet (!!). It the denser of all organic substances, it's density at 5°C equals 3.342; at the
temperatur eof +2°C, it solidifies in large shiny shards, that only melt at +5°C. the solidification, once started, continues even at 3°C. During
cristillazation, there is a very significant reduction of volume. It's dilatation coefficent is very high [...]. This compound is not atatcked by
concentrated KOH or by hot mildly-concentrated nitric acid.
The analysis leads to te following structure:
C2H2I2,
which represents the methylene iodide [...].
[...]
A few months ago, M Brüning published in the Annalen der Chemie und Pharmacie, the results his work in M Strecker's laboratory, where he describs a
product obtained by the action of ethanolic potash on iodoform. This product posses all the properties of methylene iodide: same density (3.345), same
boiling point (181-182°C), same % of carbon and hydrogen obtained by titration. But the quantity of iodine found by M. Brüning is too small, which
lead him to suggest the structure
C2H2I2O,
very unlikely for a condensation corresponding to 4 volumes of steam (?). Not having enough material at my disposition, I could not measure the vapor
density which is very simialr for both structures. [...]
Wanting to investigate the variosu products formed at the same time as methylene iodide, I evaporated the aqueous solution decanted from the oil.
After having checked it contained, apart from sodium iodide, salts of volatil organic acids, I distilled the residu with excess tartaric acid. The
distille dsolution was strongly acidic, and droplets of oil where noticed on the surface. Neutralized with Ba(OH)2, it gave afetr evaporation a
inorganic residu that I failed to cristallize. The carbon, hydrogena nd barium contents seem to indicate presence of volatils fattya cids of teh
series CnHnO4.[...]
These results indicate beyond doubt the presence of fatty acids of considerable molecular weight, being at least valerianic acid. On the other side,
we witnessed the presence of formic acid in the distillates. This synthetic formation of molecules having up to 10 or even 12 carbons by the reaction
of two compounds which contain 2 and 4 carbons, where the temperature does not exceed 100°C, seemed to me as being worth mentionning.
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The rest of the article then details the decomposition of methylene iodide, it's reaction with Ag(OAc)2 to give (AcO)2CH2 and the authors attempts to
isolate the diol HOCH2OH....
From iodoform and NaBH4:
This one really looks promising! they report 85% yield, and you only need 10% the iodoforms weight in NaBH4...
Selective reduction of polyhalomethanes by means of sodium borohydride
( http://www.springerlink.com/content/u035732314u00588/ )
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Sauron
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The springer preview gets you a psd image of first of 2 pages, including the experimental work. I have requested the full paper.
The psd is readily converted to jpg or pdf.
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jarynth
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There once was a guy named Gaylord...
There isn't much to the second page, and to the end of this tale.
Well, here it is.
Attachment: IodoformReduction.pdf (110kB)
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Sauron
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Iodoform is actually quite expensive to buy, particularly if you calculate it on a molar basis.
CHI3 $150 500 g FW 394 so about $120/mol
CH2I2 $200 500 g FW 263 so about $105/Mol
CH3I $109 500 g FW 142 $30/mol
So for this reduction to be useful on a prep scale what is needed is a good large scale prep of iodoform. The only method I have ever tried is
Vogel's, which is not very good. Org.Syn. does not have any iodoform prep, although they do have a methylene iodide prep on a 1 Kg basis that is
supposed to yield about 660 g CH2I2. The reducing agent is sodium arsenite and yields 90-97%. Sodium borohydride is a lot less toxic and yields are
almost as good.
I was looking at this as a possible route to iodomethane but it is clear that it can't compete with either I2/methanol/red P or dimethyl sulfate/KI.
Oh well.
[Edited on 12-10-2008 by Sauron]
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Sauron
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Weygand (book in forum library) cites in reference 716 a Russian prep of iodoform from 1958 using NaICl2 in 4M solution, reacted with aqueous alkiline
acetone. Fortunately a reference to CA is also given: 53, 10005 (1959).
Brauer fortunately describes the prep of KICl2 from conc aqueous KI and Cl2. I2 initially precipitates, chlorination is continued till the I2
redisolves.
This looks promising. No costly reagents. a liter of 4M KICl2 ought to give halk a Kg iodoform in theory.
[Edited on 12-10-2008 by Sauron]
Attachment: Pages from Weygand_and_Hilgetag_Preparative_Organic_Chemistry.pdf (49kB)
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Klute
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Very curious, I had never heard of NaICl2.
I guess the major drawback is the cost of iodides. It's a pity bromoform can't be reduced to dibromomethane by NaBH4 in the conditions employed int he
russian article... Maybe routher conditions, such as diborane, or NaBH4 in refluxing THF could work? Or even sodium ethoxide?
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Sauron
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Brauer cited two methods for the potassium dichloroiodide prep. The dry method is described in the attached paper from J.Chem.Soc.
The aqueous method is from Ber., in German, and has to be pulled from Wiley's greedy maw.
I had never heard of these polyhalogen salts either, and the lit. is not exactly overflowing with information about them, but there is some. The
sodium dichloroiodide is said to be less sable and more easily hydrolyzed than the potassium salt. In the case of the tetrachloroiodide, the free acid
HICl4.4H20 is also known and solid, and is prepared from conc HCl and ICl3 in stoichiometric mix.
I don't think making bromomethane is a problem by conventional methods, proceeding from bromoform would throw away too much bromine for my taste. Same
is true of iodoform, see above.
It's hard to come to come to any hard and fast conclusions until the abstract or full text of the Russian prep materializes. Mainly this is always
going to be just a route to the methylene halides for those who need them, primarily those into the methylenedioxy aromatics for whatever reasons.
[Edited on 12-10-2008 by Sauron]
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Jor
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Why make iodoform in such an exotic way? It is very easy to make from acetone, an alkali iodide and bleach (NaOCl-solution). Even if yeild is not
perfect, why do a much more difficult procedure for a little bit more yield. And yes I know iodides are expensive (but not that expensive), but time
is as well. I have prepared quite some iodoform up till now, and it was a very easy process. Only the KI is expensive, but it's not that abd for me.
Sauron, I doubt it is too expensive for you, as it is not a HAzMat shipping, and after all I recall you saying you bought soe oleum for 1000 dollar or
something like that? 100 dollar on a kilo of KI is not that bad then ? 
Then when you have iodoform, I would go through naBH4. That is expensive, but not really on molar basis. You only need a few grams to reduce 40 grams
of iodoform.
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Klute
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I guess these compounds are pretty powerfull oxidants. It would be interesting to see how they compare with straight iodine or iodine mono-chloride in
various reactions. Pretty simialr to ICl I imagine, but they look much easier to handle. I guess it's just the equivalent to ICl complexed with NaCl,
as I2 can be with NaI?
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Sauron
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See the use in US Patent RE38856 (2005) for aromatic iodinations for preparing radiographic contrast agents.
It's nice to know even obscure reagents have technological niches.
[Edited on 12-10-2008 by Sauron]
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Sauron
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| Quote: | Originally posted by Jor
Why make iodoform in such an exotic way? It is very easy to make from acetone, an alkali iodide and bleach (NaOCl-solution). Even if yeild is not
perfect, why do a much more difficult procedure for a little bit more yield. And yes I know iodides are expensive (but not that expensive), but time
is as well. I have prepared quite some iodoform up till now, and it was a very easy process. Only the KI is expensive, but it's not that abd for me.
Sauron, I doubt it is too expensive for you, as it is not a HAzMat shipping, and after all I recall you saying you bought soe oleum for 1000 dollar or
something like that? 100 dollar on a kilo of KI is not that bad then ?
Then when you have iodoform, I would go through naBH4. That is expensive, but not really on molar basis. You only need a few grams to reduce 40 grams
of iodoform. |
Vogel's recitation os the haloform reaction for iodoform is typical of such procedures, and yields only 3.5 g iodoform. In order to get 1 mol iodoform
you would have to scale up more than 100X, it's very clumsy and laborious. That's why I am willing to go the long way round the block for an
alternative that avoids the hassle.
The prices I posted are Acros ex factory, by the time I have them imported here I will pay twice that for the materials. I am not going to pay $600
for a Kg of iodoform if I can make it out of acetone, KOH, Cl2 and KI. The bill of materials for the Russian prep is same as for the haloform
reaction. The difference is in the order of addition and the dilution or in this case concentration. I do not see why you think this is "more
difficult". What is difficult about preparing a concentrated KI solution and bubbling Cl2 through it? What is difficult about preparing an alkiline
aqueeous soln of acetone? And mixing the two, slowly and cautiously? Haloforms are notorious for runaways. They are highly exothermic and involve a
delayed start (lag) which often gets people in trouble. They can be a real mess on a large scale, and a large scale is what is required to end up
with, say, half a liter of chloroform.
Above and beyond all that, the first time I made iodoform the usual way was about 40 years ago. So if I want to make it a different way, that's what
I'm going to do. Feel free to do whatever you want for your own purposes, though.
[Edited on 12-10-2008 by Sauron]
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Klute
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Jor, strangely I hardly pay more for NaBH4 than for KI  As you say, you need only
1/10 the amount of NaBH4 on a weight basis, so KI would be the most expensive compound in this prep! I really don't know why iodides are so expensive,
maybe it's because they have a somewhat limited use in industry.
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Sauron
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Jor, I don't live in the US so hazmat is meaningless to me. I avoid buying from US suppliers as much as I can for exactly that reason.
----------------
It seems that the KICl2 prepared by the "wet method" of Ephraim (see Brauer) is a monohydrate. It can also be prepared by the method of Wells et al
reported in Z.Anorg.Chem. 1, 442 (1892)and cited in J.Chem.Soc. by Allison (attached below) which for some of us may be advantageous. A slurry of KCl
in water is mixed with finely ground I2 and Cl2 passed in till all the I2 has dissolved. Orange crystals form.
This will not be much aid to those who can't obtain I2, but fortunately I don't have that problem. KCl is a lot cheaper than KI. No bromine is
needed, and anhydrous conditions do not apply.
KI is about $20/mol, 6 mols to the Kg. Obviously it takes at least 3 mols KI to make 1 mol CHI3 regardless of method.
I2 is about $30/mol, 4 mols to Kg and price per Kg almost identical to KI. It only takes 1.5 mols I2 to make 3 mols KICl2.H20 by the Wells methis. So
in principle this is about 25% cheaper. No doubt frustrating for those in USA.
[Edited on 13-10-2008 by Sauron]
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Sauron
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I have now obtained the 1917 Ber. peper by Ephraim cited in Brauer as well as the 1892 paper by Wheeler and Penfield from Z.Anorg.Chem. cited by
Allison in J.Org.Chem. Both of these methods produce the KICl2.H20 (m.p.50 C, sealed tube) rather than the anhydrous compound which whitens with
decomposition >200 C.
If anyone wants these I can post them but the recitations in English of the procedures in Brauer and in Allison appear to be accurate and complete,
and most of the papers deals with Cs and Rb compounds etc..
---------------------
Thanks to vulture for the following from C.A.
Bibliographic Information
Iodine monochloride-sodium chloride solution in the synthesis of iodo derivatives. II. Preparation of iodoform. Gengrinovich, A. I.; Simkhaev, N. G.
Pharm. Inst., Tashkent, Meditsinskaya Promyshlennost SSSR (1958), 12(No. 12), 27-8. CODEN: MPSSA9 ISSN: 0369-1586. Journal language unavailable. CAN
53:55932 AN 1959:55932 CAPLUS
Abstract
cf. C.A. 52, 7247c.
To 1 g. Me2CO is added 250 ml. H2O and 15 g. KOH, the mixt. stirred for a while and 25 ml. 4M ICl-NaCl soln. added gradually with stirring. The ppt.
formed is filtered off, washed with H2O to neutral reaction, and dried between filter paper at 30-5 to give 80-85% CHI3.
All right. So we prepare soln of 4 mols iodine monochloride and 4 mols NaCl and make up to 1 L.
Then we prepare 40 g acetone in 10 L water and 600 g KOH and we slowly add the ICl-NaOH with stirring. The FW of acetone is 58, so this is 700 mmols
on acetone basis. The yield is stated as 80-85% so we can expect about 600 mmoles iodoform. A couple hundred grams.
Iodine monochloride is a wee bit pricey to buy but easily made from the elements.
So apparently KICl2 oir NaICl2 per se is not needed, ICl-NaCl is said to work and that is easier.
So there we are!
4 mols ICl requires 2 mols I2 and 2 mold Cl2.
Brauer has prep of ICl.
Looking at the Brauer prep I am not so enthralled. It occurs to me that I have a bottle of ICl3 around here, and I bet that ICl3 + I2 -> 3 ICl,
would you not expect it to be so? Worth a second look.
Now there is a snag, my assumption that the 4M soln ICl-NaCl is in water is incorrect, ICl is insoluble in water and hydrolyzed by it. So. Is this 4M
NaCl in ICl? ICl dissolves in EtOH, Et2O, CS2, DCM. Anyway obviously this puzzle needs to be solved before proceeding. Ethanol is probably out. Ether
seems possible.
Anyone have any clue? Suggestions?
Snag unsnarled. ICl is soluble and stable in highly concentrated aqueous solutions of chlorides and in such solutions exists as ICl2- so my original
assumption of water as solvent was good after all. That's a relief.
[Edited on 14-10-2008 by Sauron]
[Edited on 14-10-2008 by Sauron]
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Sauron
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In support of my position that the 4M solution of ICl-NaCl (or NaICl2) is an aqueous one, here is a patent in which, in Example 3, you will find an
aqueous solution of >4N (which is equivalent to >4M) is employed as an iodinating reagent for a pyrolle-carbonitrile proposed as an
antifungal/anbtibacterial agent.
So, the overall proposition of low cost preparation of iodoform on a larger scale devolves to (1) availability of iodine, (2) preparation of ICl from
I2 and Cl2, and (c) conduct of the Russian procedure as described above in which 4M solution of ICl/NaCl is reacted with dilute alkiline acetone to
obtain CHI3 in 80-85% yield.
We have already established that the cost of I2 and that of KI are roughly comparable. For those who reside in iodine-challenged countries such as
USA, the conventional haloform reaction is the better way to go unless you have a large stash of I2 you are prepared to squander. But for me, this
method looks fine.
[Edited on 14-10-2008 by Sauron]
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Klute
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It looks like the preparation of ICl and KICl2 are somewhat as practical. I think I would rather chlorinate iodides directly, ratehr than doing a
chlorination and adding more I, but that's just a personel preference. As you said, it depends if one has better acces to iodine or iodides. Obviously
making I2 to latter chlorinate it is pretty wastefull.
I hope the acetone dilution cna be lessened for a bigger scale, 10l of water for 40g of acetone is... rather a lot. I guess they use such a dilution
because at the scale they work on, it wasn't problematic.
I any case, they is a very interesting topic. I'm sure using a aqueous solution of ICl2- can be very practical for halogeantions normally requiring
anhydrous conditions. It just that I don't know what to chlorinate! These conditions won't work on phenylbutanones as I would just form some iodoform
and the acid....
thanks for summarizing the refs BTW
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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Sauron
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I obtained the JACS paper from 1932 that Brauer cited, source of the ICl prep procedure. The advantage of adding I2 to liquid Cl2 is very great. The
urification is simplified, and so is getting the stoichiometry just right. If you instead pass Cl2 over solid I2 you get low yield and high impurity.
Trying to distill ICl is not very succesful, because it (like ICl3) dissociates to I2 and Cl2 at its bp at ordinary pressure. Things greatly improve
if you run a slow stream of Cl2 through during the fractionation, but the purification is still long and tedious compared to the "new process"
described.
Condensing 300 ml of Cl2 in a tared 500 ml flask and chilling it in dry ice-acetone then adding a well weighed 50% portion of I2 by stoichiometry,
gets a rapid reaction and solidification. You then remove the cooling (place it under a receiver so the excess Cl2 does not escape) and allow the ICl
crude product to come to ambient and liquid state. Since you know the tare weight of the flask and the exact mass of I2 you added, you can find the
exact mass of the Cl2 reacted, it will always be higher than calculated for ICl because ICl3 is present. Now calculate the amount of I2 needed to
convert the extra chlorine (ICl3) to ICl and add it. You are about finished. Stopper the flask (glass only!) and set it aside for at least 24 hours.
You will have more than a Kg ICl from this procedure. One or two fractional crystallizations suffice to purify it rigorously. Cool it and crystals
form; continue slowly till c.80% have crystallized, decant the supernate. Repeating this simple procedure will get you product with a freezing point
in extremely close agreement with the literature value.
The author states that he could prepare 1-2 Kg ICl in this fashion in a few hours while the "old method" took several days. This is pretty convincing.
Incidentally ICl produces very painful skin burns for which the antidote is 6M HCl. Protect yourself. Dry the Cl2 as usual, and exclude atmospheric
moisture from the flasks. If not a film of I2O5 will form.
As to dilution of acetone in the Russian procedure I would advise against trying to concentrate, this is after all still a haloform and tend to go
runaway. I have not calculated the volume required for an equivalent normal haloform reaction with say 5% hypochlorite but I think it is a good deal
larger than this. If you try to do it at 10% and muck up the cooling the flask contents will rocket out and end up all over the lab. Not good when we
are talking CHCl3 as an intermediate.
I thought I had a bottle of ICl3 but what I have is ICl, so I can try this on a somewhat smaller scale without having to generate any Cl2. I think I
have 100 g ICl on hand.
[Edited on 14-10-2008 by Sauron]
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